The present invention relates to a power supply system. More specifically, the present invention relates to a power supply system including a hybrid structure of a humidified type fuel cell and a low-grade humidified type fuel cell (non-humidified type fuel cell), and to a method of operating the power supply system.
A fuel cell is a device for allowing a power generator to generate an electromotive force by supplying hydrogen as a fuel gas and oxygen (air) thereto. In general, a fuel cell has a structure that an electrolyte film (proton conductive film) is held between gas electrodes, wherein the fuel cell is operated to obtain a desired electromotive force. Such a fuel cell is greatly expected to be applied to electric cars and hybrid type vehicles. In addition to the applications mounted on vehicles such as cars, they are now being studied to be applied to new applications different from those of existing dry cells and chargeable batteries by making effective use of an advantage of the fuel cell in terms of easy reduction in weight and size.
In general, the above-described fuel cell is typically classified based on the type of electrolytes used therefore, into a humidified type fuel cell group and a low-grade humidified (or non-humidified) type fuel cell group. Each of the humidified type fuel cell and the low-grade humidified type fuel cell has a disadvantage as well as an advantage. For example, the humidified type fuel cell can be difficult to initiate operations unless moisture is contained in outside air to some extent at the time of initial start-up because a proton conductive function of an electrolyte film of the fuel cell becomes effective only when moisture in outside air and/or moisture generated by power generating reaction are incorporated in the electrolyte film. With respect to the low-grade humidified type fuel cell (non-humidified type fuel cell), this can be started even in an extremely low humidity atmosphere, for example, at a sub-freezing temperature because the fuel cell uses an electrolyte film having a proton conductive film essentially requiring little moisture. The low-grade humidified type fuel cell, however, is difficult to be used on its own for applications requiring a large output because the electrolyte film of the fuel cell tends to be poorer in electric conductivity than the electrolyte film, having a conductive passage mainly composed of moisture, of the humidified type fuel cell.
A need, therefore, exists to provide an improved power supply system, such as a power supply system which is capable of obtaining a high output even in an extremely low temperature and low humidity atmosphere, and which is thereby suitable for portable equipment required to be operable in a wide temperature range from a sub-freezing temperature to a high temperature, and to provide a method of operating the power supply system.